1. Technical Field
The present invention relates to an analysis apparatus and an analysis method for analyzing specimens and particularly relates to a scanning atom probe which can analyze the surface of the specimens with a resolving power of an atomic level and an analysis method utilizing the scanning atom probe.
2. Background Technology
A field emission microscope (hereinafter also referred to as “FEM”) is a known apparatus that enables atomic level analysis of the surface of specimens. In the FEM, high negative voltage is impressed onto a long sharp tip of a specimen and a high electric field is generated at an apex thereof, which has a hemispheric shape. This high electric field lowers a potential barrier which confines electrons to the surface. When the electric field is sufficiently high, the width of the barrier becomes about 1 nanometer and the electrons are emitted through the potential barrier in accordance with the Heisenberg uncertainty principle. Then a tone image is displayed on a screen in front of the long and sharp tip of the sample by the incident electrons. The tone image correspondent to a work function of each area in the apex of the long and sharp tip is projected on the screen in an expanded manner because the electrons are radially emitted in the radial directions of the hemispheric apex. Magnification of the image is almost equal to ratio between radius of curvature of the apex and a distance from the apex to the screen. Assume that the radius of curvature is 100 nanometers and the distance is 10 centimeters, the magnification becomes about one million times. This magnification is high enough for observing atoms directly. Atom-by-atom observation is, however, impossible because, according to the Heisenberg uncertainty principle, uncertainty width of positions from which the electrons are emitted is larger than distance between one atom and another, and accordingly a resolving power becomes low, such as about 1 nanometer. It is, however, possible to analyze a work function and electronic state of a micro area based on an I-V characteristic of each area on the screen because the density of emission current varies widely in accordance with the work function of the emitting area.
When the atoms which are further heavier than electrons are emitted, the sufficiently high resolution can be obtained, that enables the direct atom-by-atom observation, because the uncertainty width of the emitting position becomes smaller, such as below 0.1 nanometer. A field ion microscope (hereinafter also referred to as “FIM”) enables this atom-by-atom observation. In the FIM, inert gas, such as helium or neon, is injected into a specimen vessel and positive high voltage is impressed on the long sharp tip of the specimen. An atom of the gas is field ionized right above each atom of the apex of the tip and emitted as a positive ion when an electric field generated at the apex is sufficiently high. The trajectories of the positive ions are almost same as those of the electrons in the FEM, and arrangement of the atoms on the hemispheric apex of the tip is directly projected on a screen when resolving power is increased by cooling the gas and inhibiting thermal agitation. Not only the atoms of the gas but also the atoms of the surface of the apex are emitted as positive ions if the electric field generated on the apex becomes still higher. By utilizing this field evaporation, a layer of the atoms in the surface of the apex can be separated therefrom layer-by-layer and accordingly each layer inside the apex can be sequentially observed from the surface.
An atom probe (hereinafter also referred to as “AP”) is an apparatus which enables the analysis of the compositional distribution of the evaporated area with the atomic level resolution by inletting the evaporated positive ions into the mass analysis device when the atoms in the specimen surface are field evaporated as the positive ions by the FIM. The AP has an outstanding function of detecting and identifying the atoms observed by the FIM one by one. The specimen, however, must be needle shaped similar as the specimen analyzed by the FEM or the FIM and also the apex there of must be grinded so that the radius of curvature of the apex might become below about 100 nanometers. It is not easy to grind conductive organic materials, ceramics, diamonds or the like in this manner and accordingly materials to be observed by the FEM, FIM and AP have been limited to specific specimens.
In order to solve the problem described above, the inventor of the present invention has created the scanning atom probe (hereinafter also referred to as “SAP”), which does not require the needle-shaped specimens. The technology of the SAP is, for example, disclosed in the Japanese patent application laid-open No. H7-43373. The SAP is provided with a minute funnel-shaped extraction electrode and scans over the surface of planate specimens with this extraction electrode. When there is a minute cusp of several micrometers on the specimen surface and a precise alignment of the center of an open hole at a sharp end of the extraction electrode and the apex of the cusp is obtained, a high electric field generated in a minute space between the cusp and the hole field evaporates atoms in the apex of the cusp and accordingly the SAP can analyze specimens in a manner similar to the AP.
The development of the SAP has extremely increased the variety of specimens that can be analyzed. The inventor of the present invention continuing his efforts to further improve the SAP in order that this outstanding apparatus might be utilized more widely among scientists and might bring remarkable study results.